Compositions derived by reacting polyalkene-substituted carboxylic acid, anhydride or ester compositions with amines, alcohols and/or reactive metal compounds are known to be useful additives that provide fuel and lubricating oils with improved dispersing, detergent and/or viscometric properties. The polyalkene-substituted carboxylic acid, anhydride or ester compositions are themselves useful as emulsifiers. Such polyalkene-substituted carboxylic acid, anhydride or ester compositions are commonly formed by halogen-assisted reaction of polyalkene and at least one olefinic monounsaturated mono- or dicarboxylic acid, anhydride or ester, most commonly maleic anhydride. Chlorine is the most commonly used and effective halogen. In a two-step process, as described for example, in U.S. Pat. No. 3,219,666, a polyalkene is chlorinated until there is on average at least one chloro group for each polyalkene molecule. Chlorination can be achieved by simply contacting the polyalkene with chlorine gas until the desired amount of chlorine is incorporated into the polyalkene, usually at a temperature of about 75 to about 125° C. In the second step of the two-step chlorination process, the chlorinated polyalkene product of the first step is reacted with a molar equivalent, or a molar excess of α,β-unsaturated carboxylic acid, anhydride or ester, usually at a temperature of about 100 to about 200° C. Alternatively, and as described for example by U.S. Pat. Nos. 3,215,707 and 3,231,587, a mixture of polyalkene and α,β-unsaturated carboxylic acid, anhydride or ester reactants can, in a single step process, be contacted with chlorine gas (e.g., by passing chlorine gas through the mixture with agitation) at an elevated temperature (e.g., 140° C. or above).
Polyalkene-substituted carboxylic acid, anhydride or ester compositions synthesized via halogen (usually chlorine)-induced condensation of polyalkene and α,β-unsaturated carboxylic acid, anhydride or ester compound conventionally contain a residual chlorine content of 0.5 to 1 mass %, which corresponds to 5,000 to 10,000 parts per million (ppm) of chlorine. Thus, additives derived from polyalkene-substituted carboxylic acid, anhydride or ester compounds (acylating agents) are a source of organochlorine in fuel and motor oils. Due to environmental concerns and regulations, it has become desirable to eliminate, or at least reduce, the level of chlorine and other halogens in fuel and motor oil additives and other industrial products. One way to address concerns regarding residual halogen is to avoid the use of halogen altogether by using a thermal process wherein a polyalkene and olefinic, monounsaturated mono- or dicarboxylic acid, anhydride or ester are heated together without halogen assistance, optionally in the presence of a catalyst (a “thermal” or “ene” reaction). Such a method is described, for example, in U.S. Pat. No. 3,361,673. However materials formed via the thermal route, in general, have a lower number of acylating groups per molecule. Another solution to the problem is to post-treat a halogen-containing product to remove halogen until the level of halogen in the product is at an acceptable level. Certain methods for accomplishing this are known. These methods, while capable of reducing the halogen content of the polyalkene substituted acylating agent, can also adversely reduce the number of acylating groups due to decarboxylation, manifested as a reduced saponification (SAP) number or level of active ingredient (AI), and can further increase the manufacturing time by requiring additional process steps (e.g., post-treatments or heat soaking).
U.S. Pat. No. 4,943,671 to Dockner et al, describes a reductive dehalogenation process for reducing the halogen content of an organic halogen compound with formation of a hydrogen halide in which the organic halogen compound is reacted with a hydrocarbon in the presence of elemental carbon at elevated temperature, in the presence of an iron powder or iron compound co-catalyst.
U.S. Pat. No. 5,489,390 to Sivik et al. describes a process for reducing the chlorine content of an organochlorine compound in which the organochlorine compound is mixed with (a) an acid selected from mineral acids other than HI and HBr, and organic acids having a pKa of less than about 2; and (b) a source of iodine or bromine, for a period of time sufficient to reduce the chlorine content of the compound. Chlorine levels in the compound may be reduced by treatment with iodine and bromine compounds. However, as a result, both halogens are present in the final product. Further, as would be apparent to one of ordinary skill in the art, the post treatment of dicarboxylic systems with mineral acids can lead to decarboxylation as well as the degradation of the polymer.
U.S. Pat. No. 5,672,266 to Sivik et al. discusses a process for reducing chlorine content by post thermal treatment, as in U.S. Pat. No. 5,489,390, using a relatively large amount of a Lewis acid, in the absence of elemental carbon. The Lewis acid is selected from salts of zinc, magnesium, calcium, iron, copper, boron, aluminum, tin, titanium and mixtures thereof, preferably in the presence of a source of iodine or bromine.
U.S. Pat. No. 5,885,944 to Pudelski et al. describes a method of reducing the chlorine content of polyalkylene-substituted carboxylic acylating agents which contain chlorine remaining from the chlorine induced condensation of polyalkenes and α-, β-unsaturated carboxylic acid moieties by post treatment with elemental sulfur. The method disclosed results in the formation of hydrogen sulfide as a by-product and a sulfur-containing polyalkene-substituted carboxylic acylating agent having a relatively high kinematic viscosity.
U.S. Pat. No. 6,077,909 to Pudelski et al. describes a method of providing polyalkylene-substituted carboxylic acylating agents having a reduced chlorine content, which method relies on the use of, as the polyalkene reactant, a polyolefin having a total of tetra- and tri-substituted unsaturated end groups in an amount up to about 90 mole percent, wherein the polyolefin is reacted with halogen on a molar basis up to an amount equal to the moles of tetra- and tri-substituted end groups.
EP 0 684 262 describes a process for reducing the chlorine content of chlorinated polypropylene or polyisobutylene, or a mixture of polypropylene and polypropylene succinic anhydride, or polyisobutylene and polyisobutylene and polyisobutylene succinic anhydride, in which the polymer, or polymer and succinic anhydride mixture, is treated with heat for a specified period of time.
EP 0 665 242 describes a method for reducing the chlorine content of polyalkene substituted carboxylic acylating agents which involve treatment with a halogen other than chlorine (e.g., iodine or bromine).
U.S. Pat. No. 6,562,904 to Barini et al. describe a method for reducing the chlorine content of polyalkene substituted carboxylic acylating agents in which a maleated polyalkene having a residual chlorine content is heat-soaked in an additional amount of maleic anhydride, in the absence of further added chlorine.